The present invention relates to an electric pump which is driven by a motor.
Recently, for the purpose of reducing loads on the environment, attention has been paid to an electric vehicle which is driven by outputs of a motor, and a hybrid vehicle which is driven by outputs of an engine and a motor. These vehicles are so constructed that a pump for transmission and the like which has been conventionally driven by an engine may be driven by an electric motor, because the engine is not mounted or not always actuated even though the engine is mounted. As the electric pump of this type, an electric pump in which a rotor of a trochoid pump is rotated by an electric motor has been known, as disclosed in JP-A-2005-337025
FIG. 4 is a sectional view showing a structure of the conventional electric pump of this type. The electric pump includes a motor portion 60 for driving a rotary shaft 61, and a pump section 70 composed of a pump case 71 and a pump plate 72. The pump case 71 is formed with a through hole 71a for passing the rotary shaft 61 therethrough. In addition, a holding portion 71b for holding a bearing member 62 which rotatably holds the rotary shaft 61 is formed on one side surface of the pump case 71, and a recess 71c for receiving an inner rotor 63 which is provided at a tip end of the rotary shaft 61 is formed on the other side face of the pump case 71. The pump plate 72 is arranged so as to cover the recess 71c of the pump case 71. When the rotary shaft 61 is driven to rotate by the motor portion 60, the inner rotor is rotated in the recess 71c, whereby oil introduced into the recess 71c is compressed, and the oil is supplied from the electric pump under pressure. In this manner, in the hybrid vehicle or the like, the pump is constructed by substituting an electric motor for a drive source for the rotor in the trochoid pump which has been conventionally driven by an engine.
By the way, the pump case 71 constituting the electric pump as described above has been produced by mechanical work with high precision from an aluminum die casting or a cast product as material, for the purpose of preventing leakage of liquid from the recess 71c and for the purpose of supporting the rotary shaft 61 accurately. For this reason, the pump case has become complicated in structure and high cost, and therefore, it has been desired to simplify the structure and reduce the cost. Moreover, among the electric pumps as described above, there are some pumps in which high pressure is required, such as the pump for transmission, and there are some other pumps which are used in a low pressure region, such as the electric pump for cooling the motor in the hybrid vehicle or the like. In the electric pumps which are used in the low pressure region, use of the pump case having high precision as described above is beyond a required level of sealing performance or so. Therefore, it has been particularly desired to simplify the structure of the pump case and reduce the cost.